Fairchild Semiconductor FAN53555 regulator

The FAN53555 is a step-down switching voltage regulator that delivers a
digitally programmable output from an input voltage supply of 2.5 V to 5.5 V.
The output voltage is programmed through an I2C interface capable of operating
up to 3.4 MHz.

The fan53555 interface is via I2C bus.

Required Properties:
- compatible:			Must be "fairchild,fan53555-regulator".
- reg:				The device 8-bit I2C address.
- fairchild,backup-vsel:	Register ID of backup register.
				Supported values are 0 or 1.
				The voltage selection ID used while the system
				is active will be the other option not used
				during running.
- regulator-min-microvolt:	Minimum voltage in microvolts supported by this
				regulator.
- regulator-max-microvolt:	Maximum voltage in microvolts supported by this
				regulator.
- regulator-ramp-delay:		The slew rate of the regulator, in uV/us.
				Supported values are 64000, 32000, 16000,
				8000, 4000, 2000, 1000 and 500.

Optional Properties:
- fairchild,vsel-gpio:		Present: GPIO connects to the VSEL pin and set
				the output.
				Not Present: No GPIO is connected to vsel pin.
- fairchild,restore-reg:	Present: Restore vsel register from backup
				register.
				Not Present: No restore.
- fairchild,disable-suspend:	Present: Disable regulator suspend method.
				Not Present: Do not disable regulator suspend
				method.

Example:
	i2c_0 {
		fan53555-regulator@60 {
			compatible = "fairchild,fan53555-regulator";
			reg = <0x60>;
			fairchild,backup-vsel = <1>;
			regulator-min-microvolt = <1050000>;
			regulator-max-microvolt = <1350000>;
			regulator-ramp-delay = <8000>;
			fairchild,vsel-gpio = <&msmgpio 2 1>;
			fairchild,restore-reg;
			fairchild,disable-suspend;
		};
	};
